Conventionally, pneumatic rubber vehicle tires are produced by molding and curing a green, or uncured, tire in a molding press in which the green tire is pressed outwardly against a mold surface by means of an inner, fluid expandable bladder. By this method, the green tire is shaped against the outer mold surface which defines the tire's tread pattern and configuration of sidewalls. By application of heat, the tire is cured. Generally, the bladder is expanded by internal pressure provided by a fluid such as hot gas, hot water and/or steam which also participates in the transfer of heat for curing or vulcanization purposes. The tire is then allowed to cool somewhat in the mold, sometimes aided by added cold or cooler water to the bladder. Then the mold is opened, the bladder collapsed by removal of its internal fluid pressure and the tire removed from the tire mold. Such use of the tire curing bladder is well known to those having skill in such art.
It is recognized that there is a substantial relative movement between the outer contacting surface of the bladder and the inner surface of the tire during the expansion phase of the bladder prior to fully curing the tire. Likewise, there is also a considerable relative movement between the outer contacting surface of the bladder and the inner surface of the cured tire after the tire has been molded and vulcanized during the collapse and the stripping of the bladder from the tire.
Unless adequate lubrication is provided between the bladder and the inner surface of the green tire, there is typically a tendency for the bladder to buckle resulting in a mis-shaping of the green tire in the mold and also excessive wear and roughening of the bladder surface itself. Also, the bladder surface can tend to stick to a tire's inner surface after the tire is cured and during the bladder collapsing portion of the tire curing cycle. Further, air bubbles can sometimes potentially become trapped between the bladder and tire surfaces and promote tire vulcanizing defects due to lack of adequate heat transfer.
Lubrication of the interfacial surfaces of the curing bladder and innerliner (or inner surface) of the tire can be accomplished by various methods. For example, a suitable lubricant can be applied directly to the bladder surface and/or to the tire innerliner.
Thus a lubricant can be used to pre-coat the inner surface of the green or uncured tire in order to provide lubricity between the outer bladder surface and inner tire surface during the green tire shaping and molding operation. Sometimes, such lubricant has been called a lining cement. By this method, the inner surface of the green tire, which is typically a rubber gum stock, can be simply spray-coated in a confined, ventilated, spray booth, with a lubricant which might, for example, be based upon a silicone polymer. Other additives may also conventionally be utilized in the lubricant composition, if desired, such as mica, polymeric polyols, cellulose ethers, clay such as bentonite clay and the like. Some lubricants are solvent based and some are water based. Often aqueous soap solutions are utilized. Many lubricant compositions have been taught in the art for such purpose.
Alternatively, a silicone-based lubricant can be applied to the bladder surface instead of or in combination with the application of the aforesaid lining cement.
Various silicone-based lubricant compositions have been suggested for such purposes which have sometimes been referred to as band ply lubricants. Various of the lubricants have been composed of a polyorganosiloxane mixed with various materials such as, for example, (a) polyalkylene glycol, (b) mica, (c) aluminum silicate, (d) lecithin and (e) water (U.S. Pat. No. 3,713,851); (a) mica, (b) metal silicates, (c) bentonite clay, (d) emulsifying agent and (e) lecithin (U.S. Pat. No. 3,872,038); (a) mica and (b) hydroxybutyl methyl cellulose as a thickening agent (U.S. Pat. No. 3,967,968): (a) alkylene oxide polyol, (b) mica, (c) talc, (d) bentonite clay, (e) mineral colloids, (f) suspending agent such as sorbitan ester and (g) a fatty acid such as oleic or linolenic acid (U.S. Pat. No. 4,039,143); (a) alkylene oxide polyol, (b) mica, (c) talc, (d) magnesium silicate, (e) emulsifying agent and (f) thickening agent (U.S. Pat. No. 4,043,924); (a) mica, (b) clay, (c) polyalkylene ether polyol, and (d) emulsifying agent (U.S. Pat. No. 4,066,560); and (a) mica, (b) kaolin, (c) thickener - cellulose types, (d) lecithin and (e) anionic emulsifiers (U.S. Pat. No. 4,244,742).